Getting to Grips with Curlew Sandpiper and Dunlin in
Autumn

There comes a time in every birder's life when you have to face the
frightening prospect of looking at small waders…and early autumn is that time.
From early August into September, Ireland sees large numbers of waders moving
into and through Ireland on their migration from their northern breeding
grounds. These include species like godwits and shanks but it is the small
waders (or ‘smalls’ as we birders fondly call them) that offer the greatest
challenges. Why? The problem is that there are many species that fit into the
category and they all fundamentally appear alike.

The commonest of the ‘smalls’ is the Dunlin while the very similar
Curlew Sandpiper is a regular and common autumn passage migrant. The key to
understanding their identification is in getting to know Dunlin. In fact getting
to know Dunlin makes the identification of every other member of the ‘small
tribe’ easy. However, that it not as easy as it sounds because there are
several races of Dunlin. Some have longer bills and seem larger than others. Of
course, as with all waders, there is the added complication that Dunlin vary
greatly according to their age. So, even within a group of Dunlin, there are
some birds that look very different from the others. However, there are very
obvious differences between Curlew Sandpiper and Dunlin and that’s what
we’re concentrating on here.

So, what do both species have in common? Both have black legs and
decurved black bills. On Curlew Sandpipers both the legs and bills are longer
than on Dunlin but, as already mentioned, some Dunlin (especially the race known
as alpina) can show quite long bills. So bill length, while a useful
feature, should not be the sole feature to look for when you think you have
found a Curlew Sandpiper.

ADULT
SUMMER DUNLIN

ADULT
CURLEW SANDPIPER MOULTING FROM SUMMER PLUMAGE

In early autumn, looking through flocks of smalls will reveal lots of
adult birds and both species are easy to identify when in adult summer plumage.
Dunlin show neat black belly patches, a streaked breast and face and, depending
on the race, bright rufous to reddish-brown mantles. Even when moulting from
summer to winter, the birds will usually show some black on the belly (if only
they kept that plumage all year around…life would be so much easier!). Curlew
Sandpipers are totally different to Dunlin in summer plumage in that they become
like mini-godwits adopting brick-red underparts with black, red and white
upperpart feathers. Adults when first returning in autumn will still usually
show some of their summer plumage and are easy to identify among the Dunlin
flocks. So, adults of both species are easy to tell apart when in, or moulting
from, summer plumage.

CURLEW
SANDPIPERS HAVE LONGER LEGS THAN DUNLIN AND CAN SOMETIMES WADE
CHEST-DEEP IN WATER

OR SOMETIMES EVEN SUBMERGE
THEIR HEADS COMPLETELY WHEN FEEDING

DUNLIN TEND TO FEED IN
SLIGHTLY SHALLOWER WATER

The real problem is with the identification of juvenile birds (birds born
this summer). Before looking at plumage lets look at the birds’ jizz…their
personality. Curlew Sandpipers appear more elegant than Dunlin. They seem to
stand more upright, have longer necks than Dunlin and their longer legs give
them a taller stance. Having long legs also allows them to wade into deeper
water than Dunlin and within large flocks, they are sometimes the birds wading
chest deep in water. When feeding they can often submerge their heads under the
water. They have longer more decurved bills than the longest billed Dunlin and
also have slightly longer wings than Dunlin which adds to their elongated,
elegant jizz. To my eye they also seem more methodical in their feeding
behaviour. By comparison, Dunlin seem more hunched, with shorter legs and a more
rapid, busy feeding action. Birds can’t be identified on jizz alone, so
examining the plumage is critical.

JUVENILE
CURLEW SANDPIPERS HAVE CLEANER FACES AND UNDERPARTS THAN DUNLIN

JUVENILE
DUNLIN CAN APPEAR TO HAVE QUITE ‘MESSY’ UNDERPARTS AND BROWNER, LESS
DEFINED FACE PATTERNS

It is important to remember that many of the birds you see from August
onwards will be starting to moult from their warm-coloured juvenile plumage to
their first ever winter plumage. As a result, many will show some grey feathers
on the mantle and wings (so concentrate on the warmer-edged, darker juvenile
feathers). However, in all stages of juvenile plumage, Dunlin always have very
‘messy’ underparts with heavy streaking on the brownish breast extending as
black spots and smudges onto the whitish belly and lower flanks. Even as they
develop more winter-like plumage, they can still show some spotting on the
belly. By comparison, Curlew Sandpiper appears very clean and pristine on the
underparts with a ‘peach’ wash across the breast, very faint streaking on
the sides of the breast (sometimes faint streaks on the centre of the breast)
and a clean white, unmarked belly and flanks. Even as the birds begin to moult,
the streaking is confined to just the breast sides and they often still show a
faint peach wash.

Looking at the heads of both, the clean white supercilium on Curlew
Sandpipers make the crown appear more capped and sharply defined while the pale
brownish supercilium of Dunlin makes the head appear less contrasting. Overall,
the face of a Dunlin is brownish while on Curlew Sandpiper the white chin and
white supercilium gives a much ‘cleaner’ impression. In summary, the face of
a Curlew Sandpiper is cleaner than in Dunlin with ‘crisper’, more defined
features.

FROM BEHIND, JUVENILE DUNLIN
SHOW WHITE V’S ON THE BACK

JUVENILE CURLEW SANDPIPERS
SHOW AN ‘ANCHOR’ PATTERN ON SOME SCAPULARS AND WING-COVERTS

The patterns and colours of the upperparts are also very important.
Juvenile Dunlin show a warm brown mantle with black streaking and several white
stripes forming narrow white V’s on the back. The scapular feathers (the big
feathers between the back and the wings) have black centres with rufous and
white edges. The wing coverts have greyish centres and pale brownish edges and
appear quite plain. On Curlew Sandpipers, the upperparts are a colder greyish
brown tone and lack the white V’s on the back. In fact all of the upperpart
feathers have neat pale edges giving a very scalloped or scaly appearance. Some
of the scapular feathers and the wing coverts have pale centres with a dark
central line and a dark tip almost forming an ‘anchor-like’ pattern inside
each feather. By comparison to the upperpart feathers on Dunlin, Curlew
Sandpipers are very strikingly marked.

EVEN WHEN
THE WINGS ARE DROOPED, THE WHITE RUMP ON A CURLEW SANDPIPER IS EASY TO SEE

Finally, in flight the birds are easily recognised as Curlew Sandpipers
have a clean white rump which is very obvious even at a long distance. Dunlin
show a dark broad line extending from the back, down the middle of the rump and
onto the tail. This gives the rump a dark-centred, white-edged appearance when
the bird flies. If seen well, the longer legs of Curlew Sandpipers extend just
beyond the tail in flight while the legs of Dunlin never extend beyond the tail.

JUVENILE
CURLEW SANDPIPER, ONE OF THE MOST ATTRACTIVE WADERS TO LOOK FOR IN AUTUMN

Curlew Sandpipers are one of the most attractive waders to occur in
Ireland each autumn. With a little practice, they can be very easily picked put
among the Dunlin flocks. The great thing is that they are usually with Dunlin so
direct comparisons between the two species can be made. In some years we
experience very high numbers. So, enjoy them while we have them because by
October most of them will be well on their way to their African wintering
grounds.